1. Field of the Invention.
This invention relates to gauges, and more particularly, to bore gauges for quality control applications or the like.
2. Prior Art.
The prior art is replete with various embodiments of bore measuring devices or gauges. For example, those shown in U.S. Pat. Nos. 2,720,033 (Eisele), U.S. Pat. No. 1,804,383 (Litterio), U.S. Pat. No. 1,657,326 (Steinle) U.S. Pat. No. 4,288,924 (Mizuno, et al), U.S. Pat. No. 4,507,870 (Meyer, Jr.), U.S. Pat. No. 1,658,994 (Lauer) U.S. Pat. No. 4,265,026 (Meyer), U.S. Pat. No. 2,910 781 (Bishop) and U.S. Pat. No. 3,188,744 (Bowers).
These prior art devices suffer from several deficiencies. First of all, in general, the contact anvils make point contacts with the bore wall being measured. Thus, variations in internal diameter over the length of the inner wall may exist without being detected. Further no means are provided for assuring that the internal diameter is measured at the same depth into the bore each time it is measured. In quality control applications these deficiencies may be fatal. For example, in the gas distribution industry, plastic pipes are now widely used. In joining plastic pipes it is presently common to use what is known as an "electrofusion" technique. This involves the use of an electrofusion fitting which is cylindrical in nature and has heating wires on its inner wall concentric with its own axis. The extent of intrusion of these coaxial heating wires into the central portion of the cylinder may vary from wire to wire and very close tolerances are required to effect a hermetically sealed joint between pipes With present bore gauges it is not possible to accurately check the inner diameter of such an electrofusion coupling.
Therefore, it is an object of this invention to provide an improved bore-diameter gauge which does not suffer from the deficiencies recited hereinbefore.
It is a further object of this invention to provide a bore-diameter gauge which can provide reproducible measurements which are accurate.